Books about loss for toddlers

Friends from my hometown had a baby boy a few days into May, at about 4 days old they took him back to the hopsital because his colour was off, and he wasn't sleeping or eating well. After being airlifted to a larger centre he was diagnosed with a very serious heart defect, and he did not survive. They have a 3 yr old boy as well, so I'm wondering if anyone knows of any books that might talk about death in a toddler friendly way? I plan to send them a card, and wanted to include a couple of books (he loves Cars) for their son.

I'm so sorry to hear that, my condolences to the family and your family.

I'm not sure how age appropriate it is, but MichaelRosen's 'Sad Book' is one about grief that has been recommended to me. Deb Gilori seems to be good at big concepts to me, 'No Matter What' deals with love and talks about how it endures after we're gone, this is the closest I've got with my daughter to talking about death yet. Deb Gilori also wrote 'Always and Forever' about death and grief, I'm guessing this would also be a good bet.